Embodiments of the present invention relate to collision avoidance systems.
In order to reduce the risk of midair collisions between aircraft, a system of the type known as a Traffic Alert and Collision Avoidance System (TCAS) equipment has been installed on many aircraft, such as commercial airline aircraft. In a conventional TCAS system, TCAS provides traffic advisories (TAs) and proximity warnings of nearby aircraft to flight crew, thereby assisting flight crew in seeing aircraft to avoid them. In addition, TCAS, specifically, TCAS II equipment, also provides resolution advisories (RAs), i.e., recommended escape maneuvers, to either increase or maintain vertical separation between aircraft traffic.
To generate TAs and RAs, TCAS equipment transmits radio frequency (RF) interrogation signals. The TCAS equipment then calculates slant range based on replies received from the transponders from other aircraft. Further, the replies may also include altitude information. From several successive replies, the TCAS equipment calculates a closure rate and then calculates a time to reach a closest point of approach (i.e., divide slant range by closure rate). Based on the calculated values, the TCAS equipment generates TAs and RAs to assist the flight crew in avoiding other aircraft.
When aircraft are flown in formation (e.g., military formation flights), the transponder and TCAS equipment, if so equipped, are generally placed in a standby mode so that the transponders do not respond to interrogation. Accordingly, TCAS equipment in aircraft that are not in the formation will not be able to detect aircraft in the formation flight. Likewise, aircraft that are in the formation flight will not be able to detect other aircraft whether or not these other aircraft are in the formation flight. Placing transponders into standby mode during large formation flights is desirable so as to reduce RF interference and to reduce Air Traffic Control (ATC) screen clutter due to a large number of aircraft transponders responding to ATC interrogations simultaneously.
Accordingly, a new system and method for inhibiting transponder replies to ATC interrogations during military formation flight while maintaining all other transponder and TCAS functions is needed.
A system, according to various aspects of the present invention, inhibits transponder replies to some types of interrogations during formation flight. In one embodiment of the invention, the system has a TCAS computer unit (CU) coupled to a transponder. The TCAS CU includes a flight formation detection engine that determines if the host aircraft is in a formation and if so, if the aircraft is not a tail or lead aircraft. If the host aircraft is a not a tail or lead aircraft in a formation flight, the engine also notifies the transponder to inhibit replies.
The transponder comprises an interrogation response engine that responds to all interrogations received. In addition, the response engine receives a command to inhibit replies (e.g., quiet mode command) that is sent by the detection engine. Upon receipt of such a command, the response engine will inhibit certain replies, for example, by responding to interrogations received from other aircraft and ignoring interrogations sent by ATC.
The present invention further provides a method for inhibiting transponder replies to some types of interrogations during formation flight while continuing other transponder functions. The method comprises: receiving an interrogation; classifying the interrogation according to flight formation status and type of interrogation; and responding to the interrogation in accordance with the classification.
Accordingly, by inhibiting transponder replies to ATC interrogations during formation flights and not inhibiting replies to TCAS interrogations, the system and method beneficially reduces ATC screen clutter while also reducing the risk of midair collisions between aircraft.